1. Field of the Invention
The present invention relates to an allyl chloride production process. Particularly, the invention relates to a process whereby allyl alcohol and hydrogen chloride are reacted to produce allyl chloride, an important compound used as an allyl compound starting material for epichlorohydrin, glycerin and the like, as a starting material for agricultural chemicals such as herbicides and pesticides, as a starting material for medicines such as sedatives and anesthetics, as a starting material for aromatics, as a soil enhancer, etc.
2. Description of Related Art
Allyl chloride (sometimes abbreviated hereunder as xe2x80x9cACxe2x80x9d) has conventionally been produced by chlorination of propylene. This production process, however, has serious drawbacks when employed as an industrial production process, including:
1) a high reaction temperature and production of various by-products,
2) carbonization of polymer by-products of the reaction, and clogging of reactors,
3) severe corrosion of the apparatuses due to the high temperature at which hydrogen chloride is handled, and
4) production of chlorinated organic by-products that tend to be harmful to the environment.
A method has been reported for a more industrially advantageous production of allyl chloride, whereby allyl alcohol (sometimes abbreviated hereunder as xe2x80x9cAALxe2x80x9d) and hydrogen chloride (sometimes abbreviated hereunder as xe2x80x9cHCLxe2x80x9d) are reacted in the presence of copper (I) chloride to synthesize allyl chloride (Jacques J., Bull. Soc. Chim. Fr., [5] 12, 843 (1945)). In this method, however, the reacted solution separates into an organic phase and an aqueous phase, with allyl chloride as well as a large amount of diallyl ether (sometimes abbreviated hereunder to xe2x80x9cDAExe2x80x9d) and a small amount of unreacted allyl alcohol mixed in the organic phase, and the allyl chloride yield is only about 70 wt %, which is industrially unsatisfactory.
The inventors have proposed, in Japanese Examined Patent Publication No. 6-92329, a process for production of allyl chloride whereby allyl alcohol and hydrogen chloride are reacted in the presence of a catalyst, and the allyl chloride produced is distilled off from the reaction system as the reaction progresses. This process suppresses production of diallyl ether as a by-product of the reaction, in order to give a high yield of allyl chloride.
For economic industrial application of this process, the reaction is preferably carried out in a continuous manner. xe2x80x9cContinuousxe2x80x9d means that the allyl alcohol and hydrogen chloride starting materials are continuously supplied to the reaction system, and the produced allyl chloride is continuously distilled off from the reaction system. However, since the allyl alcohol starting material will be distilled off under conditions in which the water by-product is distilled off from the reactor continuously along with the allyl chloride, it is difficult to evaporate and distill off the water from the reaction system.
For this reason, Japanese Examined Patent Publication No. 6-92329 teaches that the reaction solution may be drawn out and the excess water distilled off before it is returned to the reactor, but it discloses no concrete method for doing so. It is also mentioned that the distilled allyl chloride contains hydrochloric acid, and that this is therefore washed with weak alkali water before purifying the allyl chloride, but this method poses another problem of production of salts during the allyl chloride purification process. Another problem with the process described in Japanese Examined Patent Publication No. 6-92329 is that a high reaction temperature results in a greater amount of diallyl ether by-product.
It is an object of the present invention to provide a process for production of allyl chloride whereby allyl alcohol and hydrogen chloride are reacted in the presence of a catalyst and the resulting allyl chloride is distilled off from the reaction system, which process both suppresses production of diallyl ether as a by-product and continuously produces allyl chloride.
As a result of diligent research aimed at achieving the aforementioned object, the present inventors have completed the present invention upon the discovery that in a process for production of allyl chloride whereby allyl alcohol and hydrogen chloride are reacted in the presence of a catalyst and the resulting allyl chloride is distilled off from the reaction system, the production of the diallyl ether by-product can be suppressed by lowering the molar concentration ratio of HCL with respect to allyl alcohol in the reaction solution ([AAL]xc2xd/[HCL]).
In other words, the present invention relates to the following [1] to [8].
[1] An allyl chloride production process that comprises a) a step of supplying allyl alcohol and hydrogen chloride to a reactor and reacting them to produce allyl chloride and water, b) a step of distilling off the produced allyl chloride from the reaction system in a vapor phase and recovering it, c) a step of drawing out the reaction solution from the reactor, d) a step of distilling off and separating the water from the drawn out reaction solution, and e) a step of returning, back to the reactor, the remaining solution containing the hydrochloric acid and catalyst from which the water has been distilled off and separated.
[2] An allyl chloride production process whereby allyl alcohol and hydrogen chloride are reacted in the presence of a catalyst and the resulting allyl chloride is distilled off from the reaction system, wherein the allyl chloride production process comprises conducting the reaction in a range of 80-120xc2x0 C. and supplying the allyl alcohol and hydrogen chloride such that the molar concentration ratio of the allyl alcohol and hydrogen chloride in the reaction solution is no greater than 0.2 in terms of [allyl alcohol]xc2xd/[hydrogen chloride].
[3] The process of [2] above, wherein the organic phase containing the distilled allyl chloride is separated from the aqueous phase, and the organic phase is distilled off after extraction using water.
[4] The process of [2] or [3] above, wherein at least a portion of the aqueous phase separated from the organic phase and/or an aqueous extract of the organic phase is returned to the reactor.
[5] The process of any of [2] to [4] above, which further comprises the following three steps.
(1) A step of drawing out the reaction solution from the reactor.
(2) A step of distilling off and separating the water from the reaction solution obtained in step (1).
(3) A step of returning to the reactor the remaining solution containing the hydrochloric acid and catalyst, obtained in step (2).
[6] The process of [5] above, wherein during distillation and separation of the water in step (2), the fraction with a lower boiling point than water is recovered and at least a portion of this fraction is returned to the reactor and/or the allyl chloride purification step.
[7] The process of any of [2] to [6] above, wherein the catalyst is at least one selected from the group consisting of chlorides of transition metals, magnesium, aluminum and tin.
[8] The process of any of [2] to [7] above, wherein the reaction between the allyl alcohol and hydrogen chloride is conducted under pressure.